1. Field of the Invention:
This invention relates to motor driven cameras and, more particularly, to the structure of an operating mechanism using an electric motor as the drive source for driving the movable mirror and charging the shutter.
2. Description of the Related Art
In the conventional process for producing the ordinary camera, when the constituent parts are to be assembled in subassemblies, they are divided into two main units, namely, the mirror box and the framework having the film cartridge and takeup spool chambers.
Recently, it has been proposed to use an electric motor as the drive source both for driving the movable mirror and for charging the shutter. For this kind of motor driven camera, it has, however, been the general practice in the prior art that, although the movable mirror and the drive mechanism therefor are assembled in the mirror box unit, the shutter and the charge mechanism therefor are brought into unity with the framework, and that the motor to be used as the drive source for both mechanism takes its place in the framework. It should be pointed out here that the operation of linking the output shaft of the above-described motor to the mirror drive mechanisms can be carried out only after the mirror box unit has been put on the framework. Hence, checking of the coordination of the mirror and the shutter based on the rotation of the motor, or fine adjustment of the phases of swing turns of the movable mirror in accordance with the phase of charging and releasing motion of the shutter, which is particularly important because it affects the exposure of the camera, and testing whether or not the shutter and the movable mirror when assembled with each other actually operate with the prescribed accuracy and reliability cannot be performed, in principle, until the process comes to the final step where the mirror box unit is put together with the framework. This gives rise to a problem. So, according to the prior art, use has been made of special tools and jigs so that checking of the operations and examination of the precision accuracy may be carried out before final assembly, that is, when the mirror box unit and the framework unit are in isolation from each other. To allow for this, the maximum acceptable tolerances of the design parameters was made far more severe than necessary in view of the one-sidedness of the errors in the later assembling of the mirror box unit to the framework unit. Thus, the prescribed accuracy and reliability of coordination control of the mirror with the shutter was insured. To fulfill the requirement of setting forth such unduly severe tolerances in each subassembly, many problems were produced that the working time was prolonged, the cost was increased, and the manufacturability was impaired. Also, as a matter of course, even if no faults were found in all these tests, the final assembly should be subjected to similar tests again. Otherwise, safety could not have been heightened. This led to increase the difficulty of solving the problem of the manufacturability and cost.
In the past, the drive source for the mirror incorporated in the camera was made up by using drive and return springs. The drive spring when charged urges the mirror to move from the finder-viewing position to the exposure path-clearing position. When an electromagnet is energized, the mirror is released from a mechanical latch. When the optical path to the exposure aperture is cleared of the mirror, a mirror-up signal is produced to release the shutter. After the shutter is closed, the return spring drives the mirror to move from the non-viewing to the viewing position. In short, the so-called "quick return" mechanism was used. And, to charge this drive spring, the driving power of the motor which was common to the windup transmission system was used. In this kind of camera, therefore, besides the electric motor, there was need to use an expensive electromagnet structure as the actuator for the mirror. Further, the load on the driving of the windup transmission system became large. Therefore, not only the cost was increased, but also a far more serious problem arose that the charging speed was slowed down.
To improve upon this, a previous proposal has been made that all operation of the movable mirror is performed directly by the motor. Thus, the expensive actuator for the mirror, or the electromagnet structure, could be removed. But, a clutch was used instead as the changeover mechanism to permit the mirror to move upward to the non-viewing position when the motor rotates in the normal direction, and to move downward to the viewing position when it rotates in the reverse direction for which the windup transmission system is driven and the shutter is charged. The use of such a coordination control led to increase the minimum interval time between the successive shots. Further, as the motor was frequently overstrained, the lifetime of the motor was very shortened. Therefore, many problems were produced that a much-desired increase in the framing rate for a series of continuous shots could not be achieved in any way, and that an additional mechanism of complicated structure had to be provided for holding the movable mirror in the non-viewing position.
An attempt has been made to improve the framing rate by using two electric motors of which the first is to charge both of the mirror drive spring and the shutter and the second is to wind up the film as disclosed in U.S. Pat. No. 4,616,913 assigned to the assignee of the present invention (corresponding to Japanese Laid-open Patent Application No. Sho 61-183628 and many others whose embodiments are applied to the same mechanism). In this patent, however, because of its using the conventional form of the actuator for the movable mirror, or the electromagnet structure, the problem of the cost due to that electromagnet structure is left unsolved, although the framing rate can be improved and the lifetime of the motor can be prolonged.